Pitch blade mechanism acts on the blades of a wind turbine rotor for changing their respective angles of attack for achieving the maximum power. For this reason, blades are pivotally guided about an axis by bearings. In order to extend service life of the pitch blade mechanism, its race track and toothing have to be lubricated.
Blade pitch rotation is a function of the wind speed (low winds requires blades arranged at a minimum pitch angle and high winds requires pitch angle to be varied by rotating blades in order to change pitch angle blade angle of attack-). For both cases it is very important to perform a good lubrication on pitch bearing (race track and toothing).
Wind turbines work in different operating conditions, and therefore blade pitch activity is different for each wind turbine. Consequently, grease required for each wind turbine mechanism is also different and usually this is not optimized.
Prior art lubricating methods consist in automatically injecting grease by means of a pump system to the bearing. Known injection methods provide grease every so often regardless of the wind turbine activity and other conditions. Known lubricating methods are either manual or automatic.
A prior art manual method for lubricating a wind turbine mechanism involves completely manual operations that are programmed periodically by a maintenance service. Said operations comprise stopping the wind turbine, manually injecting grease to such mechanism by maintenance personal, and starting-up the wind turbine until the following programmed maintenance date.
WO03019004 discloses how a rotor blade of a windmill is lubricated. A lubricating grease cartridge is used that is connected by way of a feed duct to rolling bodies. Lubricant is then urged under pressure out of the lubricating grease cartridge to said rolling bearing and lubricates it. The lubricating grease which is urged out of the rolling bearing can only escape to the underside of the rolling bearing into a lubricant chamber, that grease being still used to lubricate the pitch drive.
Automatic methods for lubricating a wind turbine mechanism are carried out by using a centralized lubrication device that are installed inside the wind turbine. The device includes a pump system fitted with PLC that pumps grease from a cartridge through a circuit that distributes grease to the necessary points of the mechanism to be lubricated. The device performs a totally automatic lubricating method according a cyclic program.
U.S. Pat. No. 6,877,360 discloses a system and a method for dynamic lubrication adjustment for a lubrication analysis system. A control module is provided having a processor and sensors providing data that will be used by the processor to monitor the fluid. The processor dispenses the fluid based upon one or more parameters of the fluid.
JP63109944 refers to a method of supplying suitable amount of oil air to bearing rotating member for controlling an amount of oil supplied to a bearing of a rotating member. A programmable control unit acting on valves is provided and depends on the rotating condition of the rotating member. Oil is supplied into pipes and a timer in the programmable control unit is stopped by being operated for a suitable period of time so that the valves are closed. Therefore, lubrication is made based on a prescribed lubrication time and lubrication interval.
Providing a periodic cyclic lubrication in systems that do not have a cyclic behaviour has not proven to be advantageous. In case of a wind turbine blade pitch mechanism this is more significant since wind turbines have two differing operating thresholds, that is, with the wind turbine in power production having the blades always fixed at the same pitch angle (wind at about 0-10 m/s) or having the blades at a varying pitch angle (wind at about 11-25 m/s). These two operating thresholds require different lubricating criteria. Wind speed is a phenomenon having a non excessively cyclic behaviour (it can be said that it is at the most statistical).
It has been found that cyclic lubrication, especially in wind turbine systems, suffers from many disadvantages such as, for example, undesirable grease consumption, a limited pitch bearing life time, false brinelling effect, high costs, long time of maintenance and environmental pollutants.